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991.
Maximum Noble‐Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum
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Dr. Albert Bruix Dr. Yaroslava Lykhach Dr. Iva Matolínová M. Sc. Armin Neitzel Dr. Tomáš Skála Dr. Nataliya Tsud Dr. Mykhailo Vorokhta M. Sc. Vitalii Stetsovych M. Sc. Klára Ševčíková Dr. Josef Mysliveček M. Sc. Roman Fiala M. Sc. Michal Václavů Dr. Kevin C. Prince Dr. Stéphanie Bruyère Dr. Valérie Potin Prof. Dr. Francesc Illas Prof. Dr. Vladimír Matolín Prof. Dr. Jörg Libuda Prof. Dr. Konstantin M. Neyman 《Angewandte Chemie (International ed. in English)》2014,53(39):10525-10530
Platinum is the most versatile element in catalysis, but it is rare and its high price limits large‐scale applications, for example in fuel‐cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst’s surface. To maximize the noble‐metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria “nanopocket”, which binds Pt2+ so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt‐CeO2 nanocomposites showing high Pt efficiency in fuel‐cell catalysis we also identify these anchoring sites. 相似文献
992.
Dr. Hristiyan A. Aleksandrov Sergey M. Kozlov Dr. Swetlana Schauermann Prof. Dr. Georgi N. Vayssilov Prof. Dr. Konstantin M. Neyman 《Angewandte Chemie (International ed. in English)》2014,53(49):13371-13375
Heterogeneous catalysis is commonly governed by surface active sites. Yet, areas just below the surface can also influence catalytic activity, for instance, when fragmentation products of catalytic feeds penetrate into catalysts. In particular, H absorbed below the surface is required for certain hydrogenation reactions on metals. Herein, we show that a sufficient concentration of subsurface hydrogen, Hsub, may either significantly increase or decrease the bond energy and the reactivity of the adsorbed hydrogen, Had, depending on the metal. We predict a representative reaction, ethyl hydrogenation, to speed up on Pd and Pt, but to slow down on Ni and Rh in the presence of Hsub, especially on metal nanoparticles. The identified effects of subsurface H on surface reactivity are indispensable for an atomistic understanding of hydrogenation processes on transition metals and interactions of hydrogen with metals in general. 相似文献
993.
Konstantin V. Domasevitch 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(3):272-276
In catena‐poly[[dichloridocobalt(II)]‐μ‐(1,1′‐dimethyl‐4,4′‐bipyrazole‐κ2N2:N2′)], [CoCl2(C8H10N4)]n, (1), two independent bipyrazole ligands (Me2bpz) are situated across centres of inversion and in tetraaquabis(1,1′‐dimethyl‐4,4′‐bipyrazole‐κN2)cobalt(II) dichloride–1,1′‐dimethyl‐4,4′‐bipyrazole–water (1/2/2), [Co(C8H10N4)2(H2O)4]Cl2·2C8H10N4·2H2O, (2), the Co2+ cation lies on an inversion centre and two noncoordinated Me2bpz molecules are also situated across centres of inversion. The compounds are the first complexes involving N,N′‐disubstituted 4,4′‐bipyrazole tectons. They reveal a relatively poor coordination ability of the ligand, resulting in a Co–pyrazole coordination ratio of only 1:2. Compound (1) adopts a zigzag chain structure with bitopic Me2bpz links between tetrahedral CoII ions. Interchain interactions occur by means of very weak C—H...Cl hydrogen bonding. Complex (2) comprises discrete octahedral trans‐[Co(Me2bpz)2(H2O)4]2+ cations formed by monodentate Me2bpz ligands. Two equivalents of additional noncoordinated Me2bpz tectons are important as `second‐sphere ligands' connecting the cations by means of relatively strong O—H...N hydrogen bonding with generation of doubly interpenetrated pcu (α‐Po) frameworks. Noncoordinated chloride anions and solvent water molecules afford hydrogen‐bonded [(Cl−)2(H2O)2] rhombs, which establish topological links between the above frameworks, producing a rare eight‐coordinated uninodal net of {424.5.63} ( ilc ) topology. 相似文献
994.
In our attempt to synthesize a halogenated analog of green fluorescent protein (GFP) chromophore, we discovered a simple and efficient synthetic strategy to the derivatives of oxazole-4-carboxylic acid substituted at positions 2 and 5. The method allows for introduction of different aryl substituents at the position 5, aryl or alkyl substituents at position 2 of oxazole, and gives access not only to free carboxyl at position 4, but also to a range of its amide derivatives. The advantages of the synthetic strategy presented are availability of precursors, good yields, and avoiding palladium coupling and metalation procedures. The synthesized compounds fluoresce in visible region with quantum yields up to 0.82. We believe that 5-aryl-4-carboxyoxazole is a promising core for creation of new fluorescent dyes. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
995.
Irina Odinets Natalya Vinogradova Pavel Petrovskii Konstantin Lyssenko Tatyana Mastryukova 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1787-1791
The facile synthetic route to 5- and 6-membered 3-cyano-2-oxo-1,2-thiaphosphacyclanes and 6-cyano-2-oxa-10-oxa(thia)-phosphabicyclo [4.4.0]-decane-1-oxides was elaborated via intramolecular S-alkylation in a series of y -haloalkylsubstituted thiophosphorylacetonitriles. The compounds were used to prepare novel P(III)-containing bidentate ligands with definite stereochemistry. Diastereomeric transformations among 2-oxo-1,2-thiaphosphinanes were found and the mechanism of such transformations is suggested. 相似文献
996.
Tatyana A. Mastryukova Inga M. Aladzheva Olga V. Bykhovskaya Dmitrii I. Lobanov Alexey M. Nemeryuk Konstantin A. Lyssenko 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1701-1704
A novel convenient "one-pot" synthesis of 2-oxo-1,2 u 5 -azaphosphacyclanes 1 and 1,2 u 4 -azaphosphacyclanium salts 2 via intramolecular N-alkylation of y -halogenalkyl-substituted iminophosphoryl compounds 3 has been developed. The common nature of the reaction of intramolecular cyclization of iminophosphoryl compounds having an alkoxy group at the phosphorus atom and the Arbuzov reaction has been established. 相似文献
997.
Konstantin A. Popov Alexander M. Polozov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Diazo esters (la,b) react with trialkyl phosphates (2a–c) in the presence of BF3.OEt2 to give the corresponding phosphates (3a–e) in 42–58 % yields. The competed intra/intermolecular protonation in the reaction of la with dimethyl hydrogen phosphite leads to phosphonate. 4,and phosphite 5. 相似文献
998.
Simon Weidmann Gediminas Mikutis Konstantin Barylyuk Renato Zenobi 《Journal of the American Society for Mass Spectrometry》2013,24(9):1396-1404
In high-mass matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), the accessible m/z range is limited by the detector used. Therefore, special high-mass detectors based on ion conversion dynodes (ICDs) have been developed. Recently, we have found that mass bias may exist when such ICD detectors are used [Weidmann et al., Anal. Chem. 85(6), 3425–3432 (2013)]. In this contribution, the mass-dependent response of an ICD detector was systematically studied, the response factors for proteins with molecular weights from 35.9 to 129.9 kDa were determined, and the reasons for mass bias were identified. Compared with commonly employed microchannel plate detectors, we found that the mass discrimination is less pronounced, although ions with higher masses are weakly favored when using an ICD detector. The relative response was found to depend on the laser power used for MALDI; low-mass ions are discriminated against with higher laser power. The effect of mutual ion suppression in dependence of the proteins used and their molar ratio is shown. Mixtures consisting of protein oligomers that only differ in mass show less mass discrimination than mixtures consisting of different proteins with similar masses. Furthermore, mass discrimination increases for molar ratios far from 1. Finally, we present clear guidelines that help to choose the experimental parameters such that the response measured matches the actual molar fraction as closely as possible. Figure
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999.
The influence of “dilution” on the peculiarities of supramolecular organization in ionic crystals was analyzed by a detailed analysis of the electron density distribution function recovered by high-resolution X-ray diffraction experiments for two solvatomorphs of 4-amino-3,5-dinitropyrazole ammonium salt. The obtained results show that a decrease in the number of solvate water molecules unexpectedly increases the contribution from the anion-anion interactions to the lattice energy mainly due to the interactions between the π-systems of anions and between the nitro groups, which additionally confirms their binding nature. The latter indicates the general character of tendencies observed for hydrogen bonds and van der Waals interactions in the formation of crystalline materials in molecular and ionic crystals. 相似文献